Process and Device to Manufacture Cellulose Pulp

ABSTRACT

Process and device to manufacture and dewater cellulose pulps in which defibered cellulose is screened to remove shives, fractionated in to at least three fractions ( 10, 3, 12 ), which fractions are treated each by itself and then are brought together completely or partly, and that the fractionation is done according to specific surface, preferably with hydrocyclones, and that the process comprises process stages ( 6,7 ) that fractionates out fibers with high specific surface, preferably thin-walled fibers, and that the process comprises process stages ( 2 ) that fractionates out fibers that have lower specific surface, preferably fibers with thicker fiber wall, and that one or several fiber fractions ( 3, 3   a ) are treated, to be split, fibrillated and permanently collapsed, preferably with a refiner, ball mill or similar.

FIELD OF THE INVENTION

The present invention refer to a fiber development process and a fiberdevelopment device to treat wood fibers. One of the aims with thepresent invention is to manufacture wood containing printing grades ofpaper, news-print paper qualities and finer paper qualities (value addedgrades of paper) such as SC/LWC, from preferably TMP (thermo mechanicalpulp), CTMP or CMP. This is performed with a significant energy saving,bleaching chemicals saving and lower investment costs in washing anddewatering equipment, Another aim with the invention is to manufactureTMP, CTMP, CMP or other mechanical pulp with lower energy input, yetholding an acceptable quality of the pulp. Another aim is to by using amodified process and a modified device according to the invention totreat fiber from any pulping process for example DIP, Kraft pulp or anyother pulp and thereby saving energy and improving pulp quality amongother things. Another aim is to improve drainability and dewatering of acellulose pulp.

DESCRIPTION OF PRIOR ART

The technology that is used today to manufacture mechanical pulp such asTMP, CTMP, CMP and improved qualities of these, is with help of one ormulti-stage refining in the main line where the energy consumption is aknown problem. Thereafter a separation is done with help of screening inmultiple stages where a long fiber fraction is separated. This fractionis treated with simple or multi-stage HC (high consistency) refiningfollowed by screening stages or with screening stages in between.Possibly the refined rejects from the HC-refining can be treated with LC(low consistency) refining.

An improved process according to the above, to upgrade TMP pulp fromnews-print paper to SC/LWC pulp by using LC-refining, is previouslyknown see U.S. Pat. No. 6,361,650 B1. What is described there is asystem where one LC-refines the whole advancing pulp stream, andthereafter fractionates the stream and then treats the fractions. Thefractionation is based on length by means of slotted screens.

It is from U.S. Pat. No. 4,731,160 known to use hydrocyclones toseparate out two fractions that are bleached with hydrogen peroxide(claim 1 and claim 2).

It is from U.S. Pat. No. 5,133,832 known to bleach a long fiber fractionwith hydrogen peroxide (H₂O₂) and a short fiber fraction with dithionite(Na₂S₂O₄).

It is known from EP 1077281 A1 to use HC-refining to treat fibers(primarily recycled fibers) to arrive at a wood containing paper ofhigher quality. HC-refining is followed by slot and hydrocyclonefractionation.

Other documents which can be mentioned as references are WO 03/000982A1, WO 01 20074 A1 and WO 2004/003288 A1

PROBLEM IN PRIOR ART

The known art doesn't show how one should do to get a paper with goodsurface properties, at the same time as one saves energy and still getsa paper with good strength properties. Mechanical pulp such as TMP, canuntreated be used for finer paper qualities, but the yield is loweredand a higher energy input is required. To make finer paper qualitiestoday one can use more expensive chemical pulp fiber, such as, sulfatepulp, sulfite pulp or similar, that is mixed with mechanical pulp toachieve desired properties. The reinforcement chemical pulp has highstrength and long fibers. In none of the above mentioned documents is asystem disclosed that considers both the specific surface (fiber wallthickness) and the use of LC-refining to treat an accept fraction, toimprove a mechanical pulp of newsprint quality, different bleachingchemicals for different fractions separated on specific surface,alternatively to produce a pulp of news-print quality with aconsiderable reduction of energy, bleaching chemicals, dewatering andwashing equipment investments.

This can be concluded as that the prior art does not show clearseparation by fiber morphology allowing selective treatment of differentfractions, in conjunction with effective treatment of the fibers, orfiberfraction, responsible for paper surface stability (roughening).

General Description of the Invention

To solve the above mentioned problem a process and a device according tothe following is proposed. Process to manufacture cellulose pulps inwhich defibered cellulose is screened to remove shives, fractionatedinto at least two fractions (10,11, 12) preferably at least three, whichfractions is treated each by itself and then are brought togethercompletely or partly, characterized by that the fractionation is doneaccording to specific surface, preferably with a device (1) comprisinghydrocylones, and that the process comprises process stages (6,7) thatfractionates out fibers with high specific surface, preferably thinwalled fibers, and that the process comprises process stages (2) thatfractionates out fibers having lower specific surface, preferably fiberswith thicker fiber wall, and that one or several fiber fractions (3, 3a) are treated, to be split, fibrillated and permanently collapsedpreferably by a device that comprises some sort of milling machine (5, 5a) such as a refiner, ball mill or similar.

This has the effect that only the fibers in need of treatment because ofsurface stability problems are treated. The additional effect of thecollapsed fibers of the fibers in need of this is a better surfacestability of the paper.

According to another embodiment of the process is performed as followsProcess to manufacture cellulose pulps in which defibered cellulose isscreened to remove shives, and said pulp is then fractionated, and thatthe fractionation is done according to specific surface, preferably witha device (1) comprising hydrocylones, characterized by that the processcomprises process stages(7) that fractionates out fibers with highspecific surface, preferably thin walled fibers, and that the processcomprises process stages (2) that fractionates out fibers having lowerspecific surface, preferably fibers with thicker fiber wall, and saidpulp is fractionated into at least three fractions (10, 3, (3 a) 12),which fractions are treated each by itself and then are brought togethercompletely or partly, and that one or several fiber fractions (3, 3 a)are treated, to be split, fibrillated and permanently collapsedpreferably by a device that comprises a comminution device (5, 5 a) suchas a grinder, a refiner, a ball mill or similar.

According to an embodiment can this or those fractions (3,3 a) that aretreated in comminution device (5, 5 a comprise fibers with a z-valuebetween 0.3 and 0.8.

The effect of this is that as mentioned above only fibers in need oftreatment is treated. This gives energy saving and/or a better productin the end.

According to an embodiment can the comminution device (5, 5 a) be run sothat the fibers in the fraction at hand are collapsed permanentlythrough cracks in the fiber wall created by the comminution device.

The effect of this is that the fibers in need of treatment are lesssensitive to fiber sprinback and the surface stability of the endproduct is improved, especially when considering rewetting.

According to an embodiment can the comminution device (5, 5 a) compriserefining at a pulp consistency in the interval 0.8-14%, preferably inthe interval 1-5%.

According to an embodiment can the comminution device (5,5 a) compriseregfining at a pulp consistency of either of 0.8%, 0.9%, 1%, 2%, 3%, 4%,5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%.

According to an embodiment can the comminution device (5,5 a) compriseregfining at a pulp consistency of 3%-8%.

The effect of choosing the right interval of consistency is to get afiber development that gives permanently collapsed fibers yet notexcessive fiber cutting.

According to an embodiment can the comminution device (5, 5 a) comprisea refiner run at a energy input of 10-800 kWh/t preferably 100-600 kWh/teven more preferred 200-500 kWh/t.

The effect of running at the right energy intervals is that the fiberdevelopment and collapses are adapted to the incoming fraction so thatthe splitting, fibrillation gives the permanent collapse of the fibersneeding treatment.

According to an embodiment a fraction (10) that comprises fibers withhigh specific surface leaves from the base of a hydrocyclone stage

The effect of using hydrocyclones is that the fibers are separated onspecific surface, and fibers of different lengths can be obtained in thesame fraction.

According to an embodiment a fraction with lower specific surface (3, 3a) and more thick walled fibers that have been treated leaves from thebase of a hydrocyclone stage.

According to an embodiment the fraction (10) enriched in fines materialand comprising fibers with high specific surface is bleached in nonalkaline environment.

The effect of this is that bleaching can be adapted to the fraction inquestion. Non alkaline bleaching environment is less sensitive to beaffected by impurities in the fraction (10), said impurities cancomprise metall ions for example. Also non-alkaline bleaching can beperformed at a lower cost.

According to an embodiment the fraction (10) is bleached at a pH whichis less than 9.

According to an embodiment the fraction (10) is bleached with a reducingbleaching agent.

According to an embodiment the fraction (10) is bleached with ableaching agent comprising dithionite.

The effect of using dithionite is that the bleaching is performed at alower cost and that the dithionite is less sensitive to break downbefore it can bleach the fibers.

According to an embodiment the fraction (3,3 a) with fibers with lowerspecific surface is bleached with oxidative bleaching.

The effect of using oxidative bleaching on the fraction (3,3 a) withlower specific surface is that, this or these fraction/s has much lessof the impurities discussed above which tend to break down oxidativebleaching agents. Oxidative bleaching agents are more effective andtherefore the bleaching of this fraction (3,3 a) with these types ofbleaching agents are better with regard to brightness, of the pulp.

According to an embodiment the fraction (3, 3 a) is bleached with ableaching agent comprising hydrogen peroxide.

According to an embodiment the fraction (3, 3 a) is bleached with ableaching agent comprising ozone.

According to an embodiment the fraction (12) that remains after previousprocess stages and which has the lowest specific surface is cleaned fromsand, bark and other heavy impurities and treated, preferably with adevice (15), to peel of fiber wall of the fibers in this fraction (12)and that the device comprises some sort of comminution device such as arefiner, or similar and that the fraction after treatment completely orpartly is returned back to, preferably back ways, in the process.

According to an embodiment the device (15) refines at >15% morepreferably >14% consistency.

The effect of this is that cleaning of the pulp is performed, to removeparticles and impurities that are unwanted in the final product. In thisfraction fibers remain that are after treatment possible to use in thefinal pulp. By recovering these fibers the fiber yield is improved.

According to an embodiment the fiber stream with lower specific surface(3, 3 a), preferably with fibers with thicker fiber wall, aftertreatment is completely or partly mixed with the stream (10) of fibersand fines material with high specific surface to improve the dewateringproperties.

The effect of mixing part of or completely the fraction (3, 3 a) withthe fraction 10 is that it will be easier to extract water. The fraction10 is enriched in fibers and fines with low specific surface, thisfraction is difficult to dewater since it tend to plug filters and otherdewatering equipment and even if not plugging equipment dewatering isslow. By mixing in a fraction 10 comprising fibers with lower specificsurface, that are easier to dewater, the sum of fractions will also haveimproved dewatering properties.

According to an embodiment the fiber stream with lower specific surface(3, 3 a), preferably with fibers with thicker fiber wall, is dewateredalone to a higher consistency than the finally wanted consistency of themix of fractions, so that the fraction with fibers with high specificsurface (10), preferably thin walled fibers and fines material onlyneeds to be dewatered partly or not at all.

As mentioned above the fraction (3, 3 a) is easier to dewater. This isdue to less fines content in this fraction as well as differentproperties of the fibers with lower specific surface comprised in thisfraction. By concentration dewatering to this fraction (3,3 a) insteadof trying to dewater the fines enriched fraction (10), a more optimizeduse of the dewatering equipment can be obtained, this is among otherthings due to the lower tendency to plug the dewatering equipment. Thisaltogether makes it possible to lower investments in this type ofequipment.

According to an embodiment fractions (10, 11, 11 a) comprising fiberswith high and lower specific surface, after treatment is broughttogether to a pulp stream (32) with pulp that has been produced withlower input of energy and bleaching agents than in a conventionalfactory for wood containing printing grades of pulp, news-print pulp,SC, LWC, SC A++ pulp and other pulps.

By treating different pulp fractions in different ways a more optimizeduse of the fiber raw material is obtained.

An effect of the treatment in the process above is that fiberdevelopment performed makes the stream 32 easier to dewater on the papermachine.

To further describe, a device is disclosed to solve the discussedproblem.

Device to treat cellulose pulps to give improved properties with regardto properties such as, light scattering, tensile index, tear index,surface roughness, bleaching chemicals consumption, energy consumption,comprising a first hydrocylone device (7), a second hydrocyclone device(2), a refiner (5) and transfer devices between these, characterized bythat cellulose pulp is led to a first hydrocyclone devise (7) dividingout a base fraction (10) and an apex fraction (14) that via anotherhydrocyclone devise (2) dividing out a base fraction (3) that afterdewatering continues to further treatment with a device (5) comprisingrefiner and treatment is done at a consistency between 1-14%.

The effect of using hydrocyclones in the dividing in a device fortreating pulp is that fibermorphology is the important factordetermining what fibers will be separated from others. This means thatfiber length is not the factor on which fractionation is based as whenusing screens. This means that the device can divide out the fibers inneed for treatment.

According to an embodiment of the device a base fraction (10) isbleached with a non alkaline reducing bleaching agent.

The effect of this is that bleaching can be adapted to the fraction inquestion. Non alkaline bleaching environment is less sensitive to beaffected by impurities in the fraction (10), said impurities cancomprise metall ions for example. Also non-alkaline bleaching can beperformed at a lower cost.

According to an embodiment of the device a second base fraction (11) isbleached with an oxidizing bleaching agent.

The effect of using oxidative bleaching on a the fraction (3,3 a) withlower specific surface is that, this or these fraction/s has much lessof the impurities discussed above which tend to break down oxidativebleaching agents, oxidative bleaching agents are more effective andtherefore the bleaching of this fraction (3,3 a) with these types ofbleaching agents are better with regard to brightness.

According to an embodiment of the device an apex fraction (33) continuesto a hydrocyclone unit and is divided into a base fraction (3 a) and anapex fraction (33 a) in which said base fraction (3 a) after dewateringis treated with a refiner (5 a) at a consistency between 1-14%.

According to an embodiment of the device a base fraction (3 a, 11 a) isbleached with an oxidizing bleaching agent.

According to an embodiment of the device treated base fractions (10, 11and/or 11 a) are brought together to a common pulp stream (32) withimproved properties.

An effect of the treatment in the device is that fiber developmentperformed makes the stream 32 easier to dewater on the paper machine.

According to an embodiment of the device an apex fraction (33, 33 a)continues to cleaning with hydrocyclones (8) that removes heavyimpurities such as sand, bark, and other heavy impurities which leavesin an apex fraction (12).

According to an embodiment of the invention a base fraction continues totreatment comprising refining (15) at a consistency >5% and thisfraction is then returned in an advancing pulp stream that are led tothe inlet of the device.

Another embodiment is disclosed as a process to produce and dewatercellulose pulps in which defibered cellulose is screened to removeshives, fractionated into at least three fractions (10, 3,(3 a) 12),that the fractionation is done according to specific surface, preferablywith a device (1) comprising hydrocylones, characterized by that saidpulp is fractionated into at least three fractions (10, 3, 12), and thatthe process comprises process stages(7) that fractionates out fiberswith high specific surface, preferably thin walled fibers, and that theprocess comprises process stages (2) that fractionates out fibers havinglower specific surface, preferably fibers with thicker fiber wall thatthe fraction having lower specific surface (3, 3 a) is dewatered in adevice (5) to a given consistency, and that this fraction (3, 3 a) isthen mixed at least partly with at least one other fraction (10) beforethe mixed stream are led to the next process step.

The effect of this is that fibers that are easiest to dewater can bedewatered and then they are mixed with a fraction which is moredifficult to dewater, and the sum of fractions is a dewatered pulp.

Another embodiment of the process is disclosed with that defibering isdone through refining in one or several stages. The pulp is screened toremove larger particles. The advancing pulp stream is then led tofractionation based on specific surface, which in the case of fibersmeans by fiber wall thickness. The particles that have the highestspecific surface are sorted out first. In this fraction there are thinwalled fibers and fines particles, so called fines. This fractiondoesn't need further treatment for fiber springback (surface stability),increased strength, better surface roughness properties (bettersmothness) and so on, but can continue in the process. This fraction isbleached with a non alkaline bleaching agent, such as dithionite.Remaining pulp stream is fractionated once more on specific surface andhere fibers with lower specific surface are sorted out from fibers thathave the thickest walls and having the lowest specific surface. Thisfraction then continues to treatment with LC (Low Consistency) or MC(Medium Consistency) refining to create cracks in the fiber wall,fibrillate the fiber and collapse the fiber without affecting the fiberlength to much, i.e. there will be no significant reduction of thefiberlenght. This prevents among other things fiber springback in thefinal product. Then this fraction is bleached in an own bleaching stagewith oxidative bleaching. The remaining fraction with the lowestspecific surface is cleaned, in hydrocyclones, for example in ahydrocyclone cascade, to remove impurities such as sand, bark and otherheavy impurities. Remaining fibers with thick fiber walls continues totreatment with for example HC refining and are returned back orbackwards to the process.

Definitions

There is a prevalent grouping of fibers into early wood, summer wood andlate wood. In this document according to FIG. 1 there are a groupinginto four different fibertypes. The difference between these fiber typesare primarily the fiber wall thickness and the properties that aredependent from that, i. e. surface roughness, tensile index, moistureinduced fiber springback etc. The four fibertypes that are comprised inthis application are characterized by a z-value according to table 1 andhas been abbreviated to EEW, LEW, ELW and LLW, which means, early earlywood, late early wood, early late wood and late late wood. Thesefibertypes differ by the specific surface and on a definition basisthese can be described by the z-value, see table 1. The z-value iscalculated in the following way. $z = \frac{4\pi\quad A_{w}}{P^{2}}$

A_(W)=Fiber wall cross-section area

P=Fiber circumference TABLE 1 Fiber type EEW LEW ELW LLW z-value 0 < z ≦0.3 0.3 < z ≦ 0.6 0.6 < z ≦ 0.8 0.8 < z

In the paper industry fibers, problems are created when fibers, having az-value between 0.3 and 0.8 when paper is rewetted, for example byprinting, rise and creates a rough surface even though the paper iscalandered and has good surface properties before the rewetting.

In the document refining at different consistencies is discussed. Thedefinition of low, medium and high consistency at refining can be seenin the table below. TABLE 2 Refining LC (low) MC (medium) HC (high)Consistency <5% 5-14% >14% (% by weight)

Further down in example 2 the Rm-value is mentioned, the definition ofthis is the ratio between mass flow in the inlet to the apex flow(reject flow).

DESCRIPTION OF THE DRAWINGS

FIG. 1 Discloses the different types of fibers which are fractionatedout and treated in a process according to the invention.

FIG. 2 Discloses the core of a system according to the invention

FIG. 3 Discloses an embodiment of the core of a system according to theinvention

FIG. 4 Discloses an embodiment of the core of a system according to theinvention

FIG. 5 Discloses an embodiment of the core of a system according to theinvention

FIG. 6 Discloses an embodiment of the core of a system according to theinvention

FIG. 7 Discloses an embodiment of a complete process according to theinvention

FIG. 8 Discloses the experimental disposition according to example 1

FIG. 9 Discloses the experimental disposition according to example 2

FIG. 10 Discloses results from example 2

FIG. 11 Discloses results from example 2

FIG. 12 Discloses results from example 2

FIG. 13 Discloses results from example 2

FIG. 14 Discloses results from example 2

FIG. 15 Discloses results from example 2

FIG. 16 Discloses an embodiment of the invention according to claim 28

DESCRIPTION OF EMBODIMENTS

According to an embodiment of the core of the invention, considered tobe the best mode for carrying out the invention, disclosed in FIG. 2pulp follows the stream 13 to a hydrocyclone stage 7 with fractionatinghydrocyclones, where the incoming stream are divided up into two streams10 and 14. The stream 10 comprises fibers with a z-value between 0 and0.3 (EEW) and fines material. The stream 14 comprises fibers with az-value larger than 0.3 (LEW, ELW, LLW). This stream continues to ahydrocyclone stage 2 with fractionating hydrocyclones that divides thestream 14 into two streams 3 and 33. The stream 3 comprises fibers witha z-value between 0.3 and 0.8 (LEW, ELW).

The stream 3 continues to dewatering 4 and to treatment in a refiner 5with LC or alternatively MC-refining. In the stream 11 that leaves therefining 5 there are fibrillated, splitted and collapsed fibers. Thestream 33 comprises fibers with a z-value larger than 0.8 (LLW) andimpurities of heavier kind, the stream 33 continues to cleaning in acyclone cascade 8 optimized for cleaning away sand, bark and other heavyimpurities. The impurities leave the process and the stream 12 continuesto other treatment. The streams 10, and 11 continues to suitabletreatment such as dewatering, complex binding of metals, bleaching etc.By refining the base fraction 3 from hydrocyclone stage 2 it is possibleto process the fibers that gives the largest problem with the surfaceproperties in the final paper product and by concentrating on the streamit is possible to save energy compared with refining of the completeincoming fiber stream 13.

Furthermore the streams 10, 11 and 12 can be treated separately in asuitable way so that an optimized final product can be obtained.

According to a second embodiment which can be seen in FIG. 3 theincoming pulp 13 is divided into the streams 10, 11, 11 a and 12. Inthis case the stream 10 comprises fibers with a z-value which is lessthan 0.3 (EEW) and fines material. The stream 11 comprises fibers with az-value between 0.3-0.6 (LEW) that have been treated in a refiner (MC orLC consistency) and the stream 11 a comprises fibers with a z-valuebetween 0.6-0.8 (ELW) and which have been treated in a refiner (MC or LCconsistency). And the stream 12 comprises fibers with a z-value largerthan 0.8 (LLW). In this case it's possible to adapt the refiningconditions in 5 and 5 a even more precisely and one can for exampleadapt consistency and refining energy so that the use of the energy iseven more optimized.

According to one embodiment for a complete process shown in FIG. 7,preheated chips are washed and defibered in two refiner stages (eachstage can comprise several refiners in parallel and fewer or more thantwo stages). The pulp is diluted with water to a consistency of 3-4% andis led to latency chest, where the fibers are allowed to rest to makethem resume their shape after the refining process. The pulp is thenpumped through screens at a consistency of 1-3%, these being of slot orhole type, this is done to remove shives and larger impurities. Thereject stream from the screens are fed to the reject refining system,for example via a transfer device (not shown) to stream 12, or directlyto a device (23, 24,15, 25, 26) in the reject refining system. If thereare chemicals or other substances such as complex binders, that needs tobe washed out, the pulp is washed in a washer 22 and the pulp 13 thathas finished defibering continues to a process 1 according to theinvention.

In a hydrocyclone stage 7 a stream 10 is separated out comprising fiberswith a z-value less than 0.3 (EEW) according to FIG. 1, with help fromhydrocyclones of conventional type, for example Noss AM 80F, or otherhydrocyclones of suitable type. It's possible to imagine some other typeof equipment separating on specific surface. Fibers with a z-value lessthan 0.3 together with fines material are comprised in the pulp stream10. In this arrangement a two stage cascade is shown (6 second stage incascade) and recirculation, but here one can imagine several variants.Fibers with a z-value less than 0.3 and fines leaves in the base of thehydrocyclones 6,7. In the pulp stream 14 fibers are comprised with az-value larger than 0.3 (LEW, ELW, LLW). In the next sequence the streamcontinues into a new hydrocyclone stage 2. The base fraction 3 from thiscomprises fibers with a z-value between 0.3 and 0.8 (LEW, WLW). Thesefiber types are the ones which particularly causes fiber springback inthe finished product, which in turn creates problems with for exampleroughness. The stream 3 continues to treatment, preferably LC-refining(1-5%), alternative ways of treatment can be ball-mill, other refiningMC (5%-14%) or mills of different kind, the treatment is done to induce(create) cracks in the fiber wall, fibrillate the fiber and collapse thefiber permanently, without affecting fiber length to much. The apexfraction from the hydrocyclone stage 2 continues to a hydrocyclonecascade 8 to clean it from heavy impurities such as sand, bark and otherheavy impurities, these leaves in the apex of the hydrocyclones andleaves the process. The stream 12 from the base of these hyrdocyclonescomprises fibers with a z-value larger than 0.8 (LLW) with very thickfiber wall. These fibers' wall can not be broken easily by LC-refining5, so they continues to have the fiber wall pealed off, preferably byHC-refining or other pealing treatment and in that way the fiber wall ismade thinner, then these treated fibers are returned to the process toonce again continue through a system 1 according to the invention. Thestream 10 continues to a bleaching stage 17 where one bleaches with ableaching agent that tolerates fines material and small particles,preferably a bleaching agent that is used at non alkaline conditions (pHbelow 9), such as dithionite, for example sodium dithionite, zincdithionite, or similar. The stream 11 that comprises fibers with az-value between 0.3-0.8 (LEW, ELW) continues after adding of complexbinders to washing 27 and bleaching 16 preferably with hydrogenperoxide, ozone or other suitable oxidative bleaching agent. Bybleaching different fractions with different bleaching agents it ispossible to save bleaching chemicals and you don't need to wash as much.The oxidative bleaching agents are sensitive to for example heavy metals(e.g. Mn, Cr, Fe) that comes with the fines material, but in a processaccording to the invention the mayor part of the fines material arecomprised in the stream 10 and never continues in large amounts into thebleaching stage where the oxidative bleaching agents are used. After afurther washing 28 and 29 the fibers continues to dewatering in a discfilter 30. After that these fibers are returned and mixed with thefibers in the stream 10. By letting the disc filter 30 dewater thisfraction 11 to a higher consistency than necessary, the fraction 10 canbe more diluted and in doing so an easier dewatering of the pulp seen asa whole is obtained. The fraction 10 is difficult to dewater due tolarger contents of fines material. One could also imagine to mix a partof the fraction 11 in the fraction 10 and in doing that obtaining a pulpthat is easier to dewater if one wants to dewater 10 itself. The pulpcontinues for treatment and the paper machine to manufacture value addedpaper grades such as SC, LWC, SC-A++ and variants of these.

The system according to the invention can on detail level be arranged inseveral ways. The core of the invention is the fractionating arrangementthat preferably constitutes of hydrocyclones, but can be made from otherequipment that can fractionate on specific surface. In FIGS. 2, 3, 4, 5and 6 one can see different variants of arrangements. FIG. 2 discloses amagnification of a system where one can see that it's possible to have acascade in both the first hydrocyclone stage and/or in the second. Thedashed line shows that one can have a cascade if that is desired. FIGS.4-6 develops part what is comprised in FIG. 2, for clarity. FIG. 4discloses a single stage in both first 7 and second stage 2. FIG. 5discloses how one has a system with a single stage in first stage 7 anda cascade in the second stage 2. FIG. 6 discloses how one hashydrocyclone cascades in both first stage 7 and in second stage 2.

In another embodiment the refiner 5 is removed and the process withhydrocyclone stages (7,2 (2 a),8) remains the same, instead of treatingthe fibers after second hydrocyclonstage with a refiner, the easydewatering of the base fraction leaving this stage is the goal. A moreefficient use of the discfilter (4,4 a) is obtained, see FIG. 16. Asmentioned above the dotted lines means that cascades are optional.

EXAMPLE 1

Softwood TMP was sampled from a factory which produces paper ofnews-print quality. The sample was taken at the second stage refiner.After that the pulp was latency treated at 90° C. for 3 hours and wasthen processed in the new system. Mass flow and different fiberfractions can be seen in table 3 and FIG. 8. TABLE 3 Flow m1 m2 m3 m4 m5m6 m7 Total mass flow 100 22 78 30 48 34 14 (%) Mass flow, — — 100 39 6143 18 fractionation (%) R100 mass flow — — 100 27 75 52 23 fractionation(%) P100 mass flow 100 12 90 53 35 24 8 (%)

The reject rate of 22% in the two stage slotted screen, with slot widthof 0.15 mm, was chosen for the purpose to reduce Sommerville shives tobelow 0.1% in pulp that continued to fractionation. The pulp with lowcontents of Sommerville shives was fractionated in two-stages byhydrocyclones (Noss AM 80F) comprising a first stage consisting of atwo-stage cascade and second stage (single stage hydrocyclones). Thisarrangement allowed producing three pulp fractions with different pulpquality due to the fiber morphology (i.e. fiber cross-sectionaldimensions, specific surface).

Base 1 (m4)—accept from first stage cascade enriched in fibers with az-value less than 0.3 (EEW) and fines material. Base 2 (m8) accept fromsecond fractionation stage enriched in fibers with a z-value between 0.3and 0.8 (LEW and ELW). Apex 3 (m7) reject from second fractionationstage comprising fibers with a z-value larger than 0.8 (LLW)thick-walled fibers.

Base 2 (m8) was further refined in the LC-refiner (12″ Andritz) at threedifferent energy levels 215, 417, 504 kWh/t. The total energies for thedifferent pulps correspond to 73, 142, and 171 kWh/t for the pulp seenas a whole. The obtained unrefined and refined pulps were testedseparately. Also, pulp blends were made from Base 1 and Base 2 accordingto the pulp mass flow split in the system—47:53% (bl1, bl2, bl3).Handsheets from different pulp fractions and blends were made andtested. Dynamic de-watering tests, as well as surface roughening testswere conducted on some pulp samples. Base 1 (m4) and Base 2 (m8) andtheir blends, were bleached using dithionite and alkaline peroxide (lyeand hydrogen peroxide) in different sequences. TABLE 4 Flow m1 m2 m3 m4m7 m8 m9a m9b m9c bl1 bl2 bl3 Freeness 155 523 95 18 595 325 171 87 6435 25 86 Tensile 32.6 24.0 32.7 37.7 14.5 25.6 38.1 45.2 48.8 43.8 43.434.7 Index kNm/kg Density 401 307 416 539 299 366 455 515 550 541 568451 kg/m³ Tear 7.6 9.0 6.8 5.4 4.2 6.8 6.3 5.3 4.8 5.1 4.8 6.8 IndexNm²/kg Tensile 8.9 8.9 8.9 22.8 9.6 13.0 16.6 21.5 16.5 23.5 11.8 IndexP16/R50 kNm/kg Surface 85 235 50 20 245 135 75 50 38 35 32 50 Rougness,ml/min Specific 51 40 59 79 39 45 45 45 47 62 61 62 ScatteringCoefficient m²/kg Opacity 94.5 89.0 96.1 98.8 93.1 93.8 94.1 94.6 95.097.4 97.1 97.3 % ISO SP Filtration 8.4 — — 545 — 1.9 5.1 24.1 52.2 45.9— 34.9 Resistance ×10⁹ m/kg Stage — — — — — 215 417 504 — — — EnergykWh/t Tot — — — — — — — — — 73 142 171 Energy kWh/t

TABLE 5 m4 + m8 = bl 1 m4 + m9b = bl 2 m4 + m9c = bl 3

Physical pulp properties of different pulp fractions and their blendsare shown in table 4 and table 5. As seen, the LC refining of the Base 2fraction improves the pulp strength and sheet smoothness at a low totalcost of refining energy. Consequently, blends produced from blendsbetween Base 1 (m4) and refined Base 2 (m9 b-c) have better qualitycompared to blends made from blends between Base 1 (m4) and unrefinedBase 2(m8). This is accompanied by a relatively moderate increase in thepulp's de-watering resistance. Compared to what can be expected withHC-refining of this fraction to the same freeness.

As measured by the relative change in sheet caliper and surfaceroughness, the moisture induced fiber roughening change was 50% lower inthe sheets produced from R100 Bauer-McNett, obtained from blend 2,compared to that of the sheets produced from fibers obtained from blend1.

Also, the LC-refining improved the bonding ablility of the Base 2 longfibers to similar level as Base 1, as measured by tensile strength ofthe P16/R50 Bauer McNett fraction. This resulted in relatively high longfiber bonding ability of the blend 2 and 3.

Bleaching of Pulp According to Example 1

Before bleaching all pulps was treated in a Q-DTPA complex bindingstage. Base 2 was bleached with hydrogen peroxide and blended withunbleached Base 1 and the blend was then bleached with dithionite.

The unbleached blend of Base 1 and Base 2 (blend 1) was bleached withhydrogen peroxide in one stage.

EXAMPLE 2

Latency treated second refiner stage pulp from a factory producing TMPof news-print quality, was screened at a predetermined reject rate toremove shives and was fractionated in a two stage cascade hydrocyclonesystem. The reject rate was chosen so that 25% of the fibrous material,(25% of the R100 Bauer-McNett fiber fraction of the feed pulp), ended upin the base fraction, Base 1 (s6).

The Apex 1 fraction (s4) was further fractionated in the hydrocyclonesystem resulting in the Base 2 (s7) fraction containing 25% of thefibrous material (in percent of the initial hydrocyclone feed) and Apex2 (s5). Similarly, Apex 2 (s5) was fractionated, which resulted in Base3 (s8) containing 25% of the fiber material and Apex 3 (s9) containingat least 25% of the fiber material according to the above.

The obtained fractions Bas 1, 2 and 3 were used for further experiments.Base 2 and 3 were refined at 300 kWh/t in a LC-refiner and the pulpswhere processed in a similar way as the unrefined samples.

Base 2, 3 where split into two parts from which one part continued toLC-refining at 300 kWh/t and one part which was not refined. Theunrefined part which comprised Base 1 and the unrefined part wasdecrilled (i.e. the P100 fines fraction was removed using a Bauer-McNettfractionator). The fiber fraction was mixed with 40% fines (by weight)obtained from the second stage refiner at the TMP pulp factory. Two setsof handsheets at 60 g/m² surface weight were made. The first set of handsheets where tested according to SCAN standards.

The second set of hand sheets was cut into strips, calendered and usedfor roughening experiments. After calendering, the strips were randomlysplit into two groups. The first group was tested on tensile strength,density, porosity, surface roughness and scattering. The second group ofcalendered strips was subjected to 100% humidity at 25° C. for 3 hoursand after that was subjected to the same tests as the first group.

In FIG. 9 on can se a representation of the set according to example 2.In Table 5 the corresponding flow relationships can be studied. P 100 isadded fines fraction and how it's distributed. R 100 is the fiberfraction. It's interesting to note that Base 1 (s6) containsapproximately 60% of the P 100 fines material in the supplied pulpstream (s1). TABLE 6 Flow s1 s2 s3 s4 s5 s6 s7 s8 s9 r2 r4 r5 r9 R10072% 81% 67% — — 48% 74% 86% 87% — — — — P100 28% 19% 33% — — 52% 26% 14%13% — — — — R100 — — — — — 25% 23% 25% 27% — — — — total Rm — — — — — —— — — 0.28 0.61 0.66 0.51

In FIG. 10 there is disclosed how tensile index varies in the differentfractions. The bonding ability descends significantly for the differenthydrocyclone stages and in the last apex fraction Apex 3 (s9) thebonding ability of the fibers are very limited.

In FIG. 11 freeness related to tensile strength can be seen. As seen,Base 1 (s6) has similar strength as the base fraction Base 2 (s7), butthey have different freeness. This can be explained by the significantdifference in fines materials content between Base 1 (s6) and Base 2(s7), see table 5.

LC refining of the base fraction Base 2 (s7) and the base fraction Base3 (s8) increases the strength of these. LC refining reduces freeness ofthe pulp to some extent, but the amount of fines material that areproduced do not correspond to the slope of the regression of thefreeness-fines material relationship. The LC-refining has treated thefibers without a corresponding fines material production.

Surface roughness in Base 3 (s8) long fiber fraction (P16/R50 ml/min)was significantly reduced after LC-refining, while the bonding abilitywas increased to the same level as the long fiber fraction from Base 2(s7) see FIG. 12. Long fiber fraction of Base 2 (s7) increased thebonding ability to the same level as Base 1 (s6) after LC-refiningwithout significantly changing roughness.

Similar trends of surface roughness and strength improvement has beenobserved by producing hand sheets from a blend of Base 2 and Bas 3 wholepulp (FIG. 14). Sheets produced from Base 1 (s6) refined Base 2 (s7) andrefined Base 3 (s8) which can be seen in FIGS. 12, 13 and 14 as Mixs6+raf s7+raf s8, mixed according to the total reject rate, see table 5,exhibited a roughness value similar to the Base 1 (s6). The freeness ofthe blend was 55 ml CSF.

Base 2 and Base 3 fractions exhibited higher tendency to get increasedsurface roughness compared with Base 1, reflected in larger relativechange of the sheet caliper and surface roughness after re-wetting(FIGS. 14-15).

The propensity of the fibers to get increased surface roughness wassignificantly reduced after LC refining (FIGS. 14 and 15). Afterre-wetting, the caliper and the surface roughness changed of thecalendered sheets produced from unrefined Base 2 R100 fiber fraction andTMP fines material with 7.5% and 75% respectively. In contrast to thiscaliper and surface roughness of calandered sheets made of refined Base2 and TMP fines material changed with 1.6 and 4.4% respectively. Theunrefined Base 3 gave 10 respectively 55% and for corresponding refinedBase 3 the change was 1 respectively 11% (FIG. 15). The relative changeof the wetted sheets properties have been calculated based on thecaliper and roughness of the non-wetted sheets containing unrefined basefraction.

From the above it shall be understood that cyclone stages according tothe invention are modified according the fiber at hand to be treated. Itshould for example be understood that the person skilled in the art canput so called broken or open cascades at all or places of choice in thesystem 1. Especially it should be noted that what's given in Figuresonly are variants of what the thought of the invention is representingand the number of cyclones that are used and their physical data are aquestion of adaptation of the construction of the system to the fibersit is constructed to treat. The same goes for the concentrationconditions that are at hand in the refiners according to the inventionand pressure drop over hydrocyclone stages.

Even if this document could be seen as presuming that fiber of the samekind of wood, the invention according to the claims shall not beinterpreted as so. Mixed fibers from different wood spices can also betreated according to a system according to the invention, and a split upis performed according to specific surface of the fiber respectively.

1. A process for manufacturing cellulose pulps, the process comprising:screening defibered cellulose to remove shives; fractionating thedefibered cellulose, according to specific surface, with a devicecomprising hydrocylones, the step of fractionating comprising;fractionating out fibers with high specific surfaces; fractionating outfibers having lower specific surface, and fractionating the defiberedcellulose into at least three fractions; treating the at least threefractions individually; bringing the at least three fractions togethercompletely or partly, and using a device that comprises a comminutiondevice, to split, fibrillate and permanently collapse at least one ofthe at least three fractions.
 2. The process according to claim 1,wherein the fractions treated in the comminution device comprise fiberswith a z-value between 0.3 and 0.8.
 3. The process according to claim 1,wherein the comminution device permanently collapses the fibers of thefractions treated therein by inducing cracks in a fiber wall of thefibers.
 4. The process according to claim 1, wherein the comminutiondevice is configured to refine at a pulp consistency in the interval0.8%-14%.
 5. The process according to claim 1, wherein the comminutiondevice comprises a refiner configured to run at an energy input of10-800 kWh/t.
 6. The process according to claim 1, wherein the fractionthat comprises the fibers with high specific surface leaves from a baseof a hydrocyclone stage.
 7. The process according to claim 1, whereinthe fraction with lower specific surface leaves from a base of ahydrocyclone stage.
 8. The process according to claim 1, wherein thefraction enriched in a fines material and comprising the fibers withhigh specific surface is bleached by a bleaching agent in a non alkalineenvironment.
 9. The process according to claim 8, wherein the pH at thebleaching is less than
 9. 10. The process according to claim 8, whereinthe bleaching agent is a reducing bleaching agent.
 11. The processaccording to claim 8, wherein the bleaching agent comprises dithionite.12. The process according to claim 1, wherein the fraction with fiberswith lower specific surface is bleached with an oxidative bleachingagent.
 13. The process according to claim 12, wherein the bleachingagent comprises hydrogen peroxide.
 14. The process according to claim12, wherein the bleaching agent comprises ozone.
 15. The processaccording to claim 1, wherein a device for treatment comprising acomminution device is provided for peeling off fiber walls of fibers inthe fraction that remains after previous process stages and which hasthe lowest specific surface.
 16. The process according to claim 15,wherein the device for treatment comprises refining at greater than 14%consistency.
 17. The process according to claim 1, wherein the fractionwith fibers with lower specific surface, after treatment is mixed withthe fraction with fibers with high specific surface to improve thedewatering properties.
 18. The process according to claim 1, wherein thefraction with fibers with lower specific surface, is dewatered alone toa higher consistency than the finally wanted consistency of a mix of thefractions, so that the fraction with the fibers with high specificsurface only needs to be dewatered partly or not at all.
 19. The processaccording to claim 1, wherein the fractions comprising the fibers withhigh and lower specific surface, after treatment, are brought togetherto a pulp stream with a pulp that has been produced with lower input ofenergy and bleaching agents than in a conventional factory for woodcontaining printing grades of pulp, news-print pulp, SC, LWC, SC A++pulp and other pulps.
 20. A device for improving properties of cellulosepulps, the improved properties concerning properties such as, lightscattering, tensile index, tear index, surface roughness, bleachingchemicals consumption, energy consumption, the device comprising: afirst hydrocyclone device for receiving the cellulose pull and dividingtherefrom a first base fraction and a first apex fraction; a secondhydrocyclone device for receiving the first apex fraction from the firsthydrocyclone and dividing therefrom a second base fraction and a secondapex fraction, and a refiner for receiving and treating the second basefraction at a consistency between 1-14%.
 21. The device according toclaim 20, wherein the device is configured to bleach the first basefraction with a non alkaline reducing bleaching agent.
 22. The deviceaccording to claim 20, wherein the device is configured to bleach thesecond base fraction with an oxidizing bleaching agent.
 23. The deviceaccording to claim 20, further comprising: a third hydrocylcone devicefor dividing the second apex fraction into a third base fraction and athird apex fraction; and a second refiner for treating the third basefraction after dewatering at a consistency between 1-14%.
 24. The deviceaccording to claim 23, wherein the device is configured to bleach thethird base fraction with an oxidizing bleaching agent.
 25. The deviceaccording to claim 20, wherein the device is configured to bringtogether the first base fraction and the second base fraction to acommon pulp stream with improved properties.
 26. The device according toclaim 20, wherein the device continues cleaning the third apex fractionwith a fourth hydrocyclone that removes heavy impurities.
 27. The deviceaccording to claim 26, wherein the device is configured to refine afourth base fraction from the fourth hydrocyclone at a consistencygreater than 5%.
 28. A process for producing and dewatering cellulosepulps, the process comprising: screening defibered cellulose to removeshives; fractionating the defibered cellulose into at least threefractions, according to specific surface, with a device comprisinghydrocylones, the step of fractionating comprises: fractionating outfibers with high specific surface, and fractionating out fibers havinglower specific surface; dewatering the fraction having lower specificsurface to a given consistency, and mixing the fraction having lowerspecific surface with at least one of the other fractions.